Reframe or reframing is a way to crop a video or editing project in order to export it to a different aspect ratio. For example, you made a video project in 16:9 aspect ratio landscape/horizontal orientation but now want to make a 9:16 portrait/vertical orientation video for social media. Other forms of cropping are used primarily within a composition to remove bad edges (Crop: Source), zoom in to fill the frame (Size, Position & Rotate), add colored borders (Crop: Rectangle), or clip an overlay (Crop: Rectangle).
Reframe was added in version 24.09.
One can only add the Reframe video filter to Timeline > Output. However, for convenience there is also a Reframe button in Export > Video
(Resample is typically used to change the resolution without changing aspect ratio. But one can use it and change aspect ratio in order to intentionally add black bars. For example, you compose a very wide film aspect ratio of 2.4:1 but want to deliver it as 16:9–letterboxing.)
Clicking Reframe adds the filter to Output or switches the user interface to it:
You can drag this rectangle control around and resize it to even dimensions only (for codec and pixel format compatibility), but you cannot push any part of the rectangle outside of the frame.
It supports keyframes and motion tracking. However, if you change the size, only the size at the beginning is used. Here, I tracked the white horse in the first clip only and then re-centered it.
There are presets for 9:16 (defaults), 16:9, 4:3, and Square.
You can save the Reframe filter on your project and simply disable it when you want to export without it. You can have multiple Reframe filters and the first enabled one is used on export.
The black bars you see in this embedded player are not part of the video!
Here it is on YouTube Shorts